[PATCH] perf-script: check session->header.env.arch before using it

[Song Liu <songliubraving@fb.com>]

When perf.data is not written cleanly, we would like to process existing
data as much as possible (please see f_header.data.size == 0 condition
in perf_session__read_header). However, perf.data with partial data may
crash perf. Specifically, we see crash in perf-script for NULL
session->header.env.arch.

Fix this by checking session->header.env.arch before using it to determine
native_arch. Also split the if condition so it is easier to read.

Cc: stable@vger.kernel.org
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 tools/perf/builtin-script.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 6211d0b84b7a6..7821f6740ac1d 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -4039,12 +4039,17 @@ int cmd_script(int argc, const char **argv)
 		goto out_delete;
 
 	uname(&uts);
-	if (data.is_pipe ||  /* assume pipe_mode indicates native_arch */
-	    !strcmp(uts.machine, session->header.env.arch) ||
-	    (!strcmp(uts.machine, "x86_64") &&
-	     !strcmp(session->header.env.arch, "i386")))
+	if (data.is_pipe)  /* assume pipe_mode indicates native_arch */
 		native_arch = true;
 
+	if (session->header.env.arch) {
+		if (!strcmp(uts.machine, session->header.env.arch))
+			native_arch = true;
+		else if (!strcmp(uts.machine, "x86_64") &&
+			 !strcmp(session->header.env.arch, "i386"))
+			native_arch = true;
+	}
+
 	script.session = session;
 	script__setup_sample_type(&script);
 
-- 
2.30.2